A conventional product packaging machine which utilizes a heat sealable film, moves both the product and the film in a longitudinal direction, bonds the film edges together to form a tube around the product and seals the tube transversely has generally the construction shown in FIGS. 11 and 12. The term "product" is used to refer to any product, item, material or anything else that might be packaged by the type machines being presently and hereafter described. Referring further to FIGS. 11 and 12, a thermoplastic film in a roll 1 supported by rolling shafts 2 is supplied by a pullout roller 3 and a tension belt 4 and establishes film tube 7 of this belt-like film 5 by passing it over a cylinder making former 6. A continuous stream of to-be-wrapped products 10 are supplied, equidistantly spaced, into the tubular film 7 by the pushing force of attachments 9 disposed on endless chains of a chain conveyor 8, and the tubular film 7 is clamped and fused transversely between the to-be-wrapped products 10 by a pair of seal bars 11, 12 disposed transversely across the tubular film 7.
As seen in FIG. 12, a lever 15, supported pivotally by a pin 14 on a machine frame 13, is connected by a link 18 to a reciprocating frame 17, supported slidably on a guide 16, and the lever 15 is caused to swing back and forth by the rotation of a grooved cam 19. Accordingly, the reciprocating frame 17 reciprocates along the guide 16 as represented by an arrow. On the other hand, the seal bars 11, 12 connected by links 21, 22 are brought close to, and then away from, one another by the rocking operation of the bell crank 20 as generated by internal mechanism (not shown). Consequently, the seal bars 11, 12 move along a pair of elliptical paths as represented by an arrow 23 in FIG. 11 enabling a transverse sealing of tubular film 7 for an extended time.
When the length of the to-be-wrapped products 10 sent by the chain conveyor 8 is changed, a sensor 24 reads the length of the to-be-wrapped products 10 and inputs this length value as a digital value to a microcomputer 25. The microcomputer 25 generates signals 26, 27 corresponding to the length of the to-be-wrapped products by its arithmetic operation. Signal 26 is sent to a first motor 28 (FIG. 11) and the signal 27 is sent to a second motor 29 (FIG. 12). These motors change the rotating speeds of the pullout roller 3, the tension belt 4 and the grooved cam 19. In other words, since a third conveyor drive motor 30 in FIG. 11 always keeps a fixed speed to drive products through the machine, the film speed must be lowered in the case of a product 10a having a small length in order to keep constant the gaps 31, 32 between the adjacent products 10b in FIG. 13, and the film speed must be increased, on the contrary, in the case of a product 10b having a greater length. The reciprocating speed of the seal bars 11, 12 is synchronized with the film speed thus changed.